The atmospheric phenomenon will pack a chilly one-two punch this week

If you’re the type of person who piles on the blankets at the slightest hint of cold, take a deep breath—this may be hard to swallow. The United States has enjoyed an unseasonably warm autumn, but that’s about to change. Starting today, a polar vortex is poised to bring bitter cold temperatures to much of the United States, reports Doyle Rice for USA Today.

The National Weather Service Climate Prediction Center is warning of a pending polar vortex—a phenomenon that occurs when an area of low pressure and icy air surrounding both poles expands. The chill will come in two waves, writes the NWS, plunging much of the U.S. into bitter cold.

“Polar vortex” sounds (and feels) dramatic, but it’s actually a term that’s long been used by weather forecasters. As the NWS explains, the phenomenon is caused by strong air flow that usually keeps cold air close to the poles. On occasion, though, that strong circulation weakens, causing the cold air to spread out and expand south. The jet stream that usually sweeps across the northern edge of the U.S. is forced south, bringing the cold air along with it. The result: a pocket of frigid air that can engulf a city for days.

This polar vortex isn't a surprise to forecasters, but it may come as a nasty shock to people who remember the last one all too well. In January 2014, a polar vortex enveloped much of the country, contributing to record lows throughout the nation and freezing a massive 75 percent of the Great Lakes. However, the wretched winter that produced so much snow in Boston last year wasn’t due to a polar vortex; rather, the nearly 109 inches of snow that fell during the winter of 2014-15 is thought to have occurred in part because of warm ocean temperatures.

While the Midwest braces itself for what Rice calls “life-threatening cold temperatures and fierce winds” and the rest of the country wonders what the polar vortex will bring, it’s worth asking whether climate change will affect the vortex in the future. While researchers are still learning about the phenomenon, it’s thought that the jet stream is becoming more wavy over time as the Arctic warms.

As Caitlyn Kennedy of NOAA writes, a wavier jet stream means that polar air gets sucked further south than usual—and even though the connections between global warming and the polar vortex must be studied further, the speed of climate change could mean that more vortices are on the way. So grab your mittens and hunker down—it could be a wild (and very cold) ride.

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About Erin Blakemore

Erin Blakemore is a Boulder, Colorado-based journalist. Her work has appeared in publications like The Washington Post, TIME, mental_floss, Popular Science and JSTOR Daily. Learn more at erinblakemore.com.